In the field of subsea hydrocarbon production, the formation of hydrates and/or wax deposits is a well known problem. At low temperatures hydrocarbons may solidify and limit or block the flow in the subsea pipelines. One known measure is to insert inhibitors into the flowing well stream, such as MEG.
Another method includes ensuring a certain temperature of the flowing fluid. This is for instance achieved with a method referred to as direct electrical heating (DEH). The method involves arranging a cable along a steel pipe and connecting it to the steel pipe at two distant positions. By applying an alternating current to the cable, and thus also through the steel pipe, the latter becomes heated due to both ohmic and inductive power dissipation. The DEH method is often employed to heat pipelines of several kilometers of length. International patent application WO2007011230 describes such a solution.
In addition to heating long lengths of flow lines, one will sometimes need to heat smaller subsea components such as a Xmas tree or a shorter length of pipe. Sometimes one also wants to heat a specific part of a pipeline more extensively than what is possible with the installed DEH components. Patent publication U.S. Pat. No. 6,278,095 describes a solution where an electric cable is wound around a subsea component which shall be heated as an induction coil (cf. the jumper 27 in FIG. 5 of the said publication). Electrical power is supplied to the induction coils from current flow in the walls of the heated segment of pipeline or from an external source such as a subsea transformer or ROV.
U.S. Pat. No. 6,371,693 describes (in FIG. 9a) a toroidal transformer used to extract electrical power for small electrical loads, such as heating of pipeline jumpers, operating equipment or other purposes subsea.
Patent application publication US20100101663 A1 describes heating of a pipeline by using the inherent resistivity of its electrically conductive sections. In addition it describes using the pipeline as a power distribution line to provide auxiliary power to remote pipeline locations.
German publication DE102008056089 A1 describes a method of measuring the condition of a pipeline, typically an offshore pipeline.